Triaxial antenna



Dec. 17, 1968 w. w. BLACK TRIAXIAL ANTENNA 5 Sheets-$heet l aged April25. 1966 INVENTOR. flaaeow #14 544cm Dec. 17, 1968 w, w, BLACK 3,417,400

TRIAXIAL ANTENNA filed April 25, 1966 5 Sheets-Sheet 3 INVENTOR. WaoaeonW54 AVG/Q lmeviw United States Patent TRIAXIAL ANTENNA Woodrow W. Black,Los Angeles, Calif., assignor, by mesne assignments, to the UnitedStates of America as represented by the Administrator of the NationalAeronautics and Space Administration Filed Apr. 25, 1966, Ser. No.544,895 9 Claims. (Cl. 343-771) The present invention relates toimprovements in antennas, and more particularly to a novel, transverselypolarized triaxial antenna.

Prior art antennas are of a variety of configurations, including coaxialantennas having post feed slots and the clover leaf type of antennas.Although these antennas have presented certain improvements in the artstill further improvements are needed.

In this respect the present invention is directed to a horizontallypolarized antenna arragement of simplified construction providingimprovements in pattern and impedance matching.

One object of this invention is to provide an improved transversely orhorizontally polarized antenna.

Another object of this invention is to provide an improved antenna ofthe character referred to applicable in the construction of a phasedarray transmitting antenna.

Another object of the present invention is to provide a simple, compact,transversely polarized antenna of improved construction which isinexpensive and relatively easy to manufacture.

A further object of this invention is to provide an improved antenna ofthe character referred to which is capable of generating anomnidirectional radiation pattern.

The foregoing and other objects and advantages of this invention areachieved in a triaxial antenna construction according to this inventioncomprising a shorted, coaxial, TEM mode transmission line which includesan elongated inner conductor, a tubular intermediate conductor disposedabout the inner conductor and provided with predetermined feed slotconfigurations. This transmission line is disposed within an outertubular conductor which is provided with at least one elongatedradiating slot which substantially parallels the inner conductor. Theantenna is designed to provide a toroidal pattern with gainperpendicular to the axis of the antenna. It is horizontally ortransversely polarized which minimizes reflections from adjacent antennaelements. The pattern has low side lobes and can be made to approach themaximum gain-bandwidth configuration. The feed slots of the intermediatetubular member of the antenna excite one or more long radiating slots inthe outer tubular member or conductor of the antenna. The feed slots maybe of various configurations characterized by having a portion such as acenter section portion which is in line with or substantially parallelto the axis of the antenna element. The slots may be arranged to definea slot path around the intermediate conductor or pluralities of theslots may be arranged in axially spaced positions. The length of theradiating slot or slots may be expressed as where M is any whole number,for example, 1, 2, 3, etc.

The foregoing as well as other objects and advantages of the presentinvention may be more clearly understood by reference to the followingdetailed description when considered with the drawings which, by way ofexample only, illustrate different forms of antenna construtcionembodying the advantages and features of the present invention.

3,417,480 Patented Dec. 17, 1968 ice In the drawings:

FIGURE 1 is an elevational view, fragmentarily in section, of oneembodiment of the antenna of the present invention showing a triaxialconfiguration comprising an inner conductor, an intermediate tubularconductor and an outer tubular conductor;

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged elevational view, fragmentarily in section, of aportion of an inter-mediate tubular conductor illustrating a feed slotconfiguration differing from that of FIGURE 1;

FIGURE 4- is a sectional view taken along the line 4-4 of FIGURE 3;

FIGURE 5 is an elevational view drawn to the scale of FIGURE 1 of aportion of an intermediate conductor usable in the construction ofFIGURE 1 and showing a different configuration of feed slots;

FIGURE 6 is an enlarged sectional view taken along the line 6-6 ofFIGURE 5;

FIGURES 7 and 8 are enlarged longitudinal sectional views, respectively,of selected portions of the antenna construction illustrated in FIGURE 1for the purpose of demonstrating the theoretical concept explaining howenergy which is propagated axially of the inner and intermediateconductors is transformed into energy radiating transversely andcircumferentially from the outer conductor;

FIGURES 9 10 and 11 are sectional views taken along the respectivesectional lines 9-9, 10-10 and 11-11 of FIGURE 8 illustrating thecurrent and voltage conditions within the antenna construction in planesplaced in quarter wavelength intervals from each other.

In the drawings, the triaxial antenna construction is representedgenerally by the numeral 10 and comprises a tubular, outer conductor 12receiving one end of a shorted, coaxial, TEM mode transmission line 14.The transmission line 14 includes an elongated inner conductor 16 and atubular intermediate conductor 18 having a series of complex feed slots28 formed therein. In the operation of the antenna 10, the feed slots 20excite one or more axial, radiating slots 22 in the outer conductor 12causing the outer conductor to circumferentially radiate electromagneticenergy transverse to the axis of the antenna 10, and preferably in anomnidirectional radiation pattern in a plane perpendicular to theantenna axis.

More specifically, in the form of the shorted coaxial line 14illustrated in FIGURE 1, the inner conductor 16 is an elongatedcylindrical metal body, While the intermediate conductor 18 is a hollowmetal cylinder surrounding the inner conductor and separated therefromby a plurality of insulating rings 24. An electrical short 26 isconnected between the intermediate and inner conductors 18 and 16adjacent one end thereof and preferably takes the form of a metal ringstationed around the inner conductor with an outer edge bearing againstthe inner wall of the intermediate conductor.

Ends of the inner and intermediate conductors 16 and 18 opposite theelectrical short 26 are received by a connector 28 for coupling energyto the antenna 10. The connector 28 is of a conventional type andincludes an outer sleeve 30 having an internal collar 32 and aninternally threaded end portion 34. The collar 32 supports an annularinsulating head 36 for holding an end portion 38 of the inner conductor16 within the connector 28, and acts as an end stop for an enlarged endportion 40 of the intermediate conductor 18, including an externallythreaded collar 42 mating with the internally threaded portion 34 of thesleeve 30. Electrical energy applied to the connector 28 causes thecoaxial transmission line 14 to transmit TEM modes while the electricalshort 26 establishes a standing wave pattern within the line includingtwo separate series of one-half wavelength separated maximum current andvoltage regions, the maximum current regions being spaced one-quarterwavelength from the maximum voltage regions and the electrical short 26being located at a maximum current region.

It is well known that the TEM mode will not excite axial slots, such asthe axial radiating slots 22 in the outer conductor 12. Therefore, toexcite the radiating slots, the intermediate conductor 18 includes oneor more series of complex feed slots 20. In the form of the antenna 10illustrated in FIGURE 1, three series of feed slots are included and areequally spaced fro-m each other around the intermediate conductor.

Generally speaking, the feed slots 20 are substantially one-halfwavelength long and each includes an axial portion 44 substantiallyparallel to the inner conductor 16 and a transverse portion 46 extendingfrom the associated axial portion and lying immediately adjacent amaximum current region. Also, the feed slots 20 are spaced substantiallyat multiples of one-half wavelength along the intermediate conductor 18and transverse portions of even multiple feed slots are reversed indirection from transverse portions of odd and multiple feed slots (ifany).

More particularly, in FIGURE 1, the feed slots 20 are generally U-shapedhaving relatively long axial portions 44 and relatively short transverseportions 46 at opposite ends of and substantially normal to the axialportions. Also, corresponding feed slots 20 in the three series of slotsare aligned as groups with the transverse portions 46 of slots of eachgroup extending in the same direction around the intermediate conductor18.

As illustrated most clearly in FIGURES 7 through 11, the centers of theaxial portions 44 are immediately adjacent maximum voltage regions whilethe maximum current regions lie between the transverse portions 46 ofadjacent feed slots 20. Thus arranged, axial currents in the coaxialline 14 along the inner surface of the intermediate conductor 18 excitethe transverse portions 46 of the feed slots 20 to induce voltagethereacross. Voltages induced across the transverse portions 46 aretransposed 90 by the axial portions 44 of the feed slots to be of likeinstantaneous polarity in each axial portion and to inducecircumferential currents of like direction around the outside of theintermediate conductor 18. The fields resulting from the circumferentialcurrents, in turn, excite the axial radiating slots 22 in the outerconductor 12 to circumferentially radiate electromagnetic energytransverse to the axis of the antenna 10 and preferably in anomnidirectional radiation pattern as the antenna is rotated.

In this regard, the outer conductor 12 is a hollow metal cylinder andthe axial slots 22 are each a multiple of onehalf wavelength. Also,electrical shorts 48 and 50 are included adjacent opposite ends of theouter conductor 12 and between the outer and intermediate conductors andpreferably comprise annular metal plugs seated around the intermediateconductor 18 at the ends of the outer conductor. The plugs and outerconductor define an annular chamber 52 around the intermediate conductor18 which is substantially a multiple of one-half wavelength long withthe electrical short 48 being substantially a multiple of onehalfwavelengths beyond the middle of the endmost feed slot 20.

With the outer conductor 12 thus arranged, the circumferential currentsbetween the intermediate and outer conductors excite the radiating slots22 in the manner illustrated in FIGURES 7 through 11. In particular, acontinuous sheet of current is induced along the outside of the outerconductor 12 which changes in direction at times corresponding to eachhalf cycle, and electromagnetic energy radiates circumferentially fromthe outer conductor transverse to the axis of the antenna 10 and in anomnidirectional radiation pattern as the antenna is rotated around itslongitudinal axis.

In the foregoing operation, the outer conductor 12 also acts as apolarizer for the antenna 10, blocking the exit of any cross-polarizedenergy from the antenna, that is, energy other than that radiatingcircumferentially and substantially normal to the axis of the antenna.

From the foregoing, it is appreciated that the present inventionprovides a compact, transversely polarized, omnidirectional antennadesign which is inexpensive and relatively easy to manufacture andassemble.

Within the basic framework of the triaxial antenna previously described,numerous changes and modifications may be made without departing fromthe spirit of the invention. For example, various numbers andcombinations of feed and radiation slots may be employed. The length andangle of the slots may be altered relative to each other. Also, thedesign of the feed slots may be changed.

One such example of feed slot design change is illustrated in FIGURES 2and 3 and another in FIGURES 4 and 5. In FIGURES 2 and 3, the feed slots20 are generally Z-shaped having transverse portions 46 extending fromopposite ends of and back along the axial portions 44'. The Z-shapedslots are substantially one-half wavelength long and are spaced atmultiples of one-half wavelength with the transverse portions of evenmultiple feed slots being reversed in direction from the transverseportions of odd multiple feed slots.

As in the U-shaped slots, the transverse portions 46' are immediatelyadjacent maximum current regions. In fact, the maximum current regionsare preferably located at the center of the axial portions 44'. Thismeans that for the Z-shaped slot configuration, the electrical short 26'is spaced a multiple of one-half wavelength from the middle of theendmost Z-slot rather than an odd multiple of a quarter wavelength, aswith the U-shaped feed slots.

With the Z-shaped slots and electrical short 26 thus spaced along theintermediate conductor 18', the mode of excitation of the feed slots andhence of the antenna 10 is very similar to that previously described. Inparticular, axial currents in the maximum current regions along theinner surface of the intermediate conductor 18 excite the transverseportions 46 to induce voltages thereacross. The voltages are transposedin direction normal to the antenna axis by the axial portions 44 andbecome of like instantaneous polarity in each axial portion. Thevoltages in axial portions, in turn, induce circumferential currents oflike direction around the intermediate conductor which excite theradiating slots 22 of the associated outer conductor as described inconnection with FIGURES 7-11.

In FIGURES 5 and 6, one or more axially extending zigzag slots 54 arespaced equally from each other around the intermediate conductor 18".The slots 54 have portions conforming to half wavelength feed slots withaxial portions 44" and transverse end portions 46". In fact, the slots54 may be considered as being formed of a series of feed slots of thegeneral design previously described joined end to end. That is, the feedslot portions are spaced onehalf wavelength apart with the transverseportions 46" of even multiple feed slot portions reversed in directionfrom the transverse portions of odd multiple feed slot portions. Also,the transverse portions are immediately adjacent maximum current regionsin the conductor 18" and the mode of exciting the slots to excite theradiating slots is as previously described for the U-shaped feed slots.

In viw of the foregoing as well as other changes and modifications whichmay be made in the illustrated forms within the spirit of the presentinvention, it is intended that the invention be limited in scope only bythe terms of the following claims.

I claim:

1. A transversely polarized triaxial antenna, comprising:

a shorted coaxial TEM mode transmission line including an innerelongated conductor, a tubular intermediate conductor substantiallycoaxial with and receiving said inner conductor, and first short meansadjacent a first end of said intermediate conductor and between saidintermediate and inner conductors responsive to electrical energyapplied to a second end of said line for setting up a standing wavepattern in said line including separate series of one-half wavelengthspaced maximum current and voltage regions;

said intermediate conductor including a series of complex feed slots inits outer wall, each being substantially one-half wavelength long andeach having an axial portion substantially parallel to said innerconductor and a transverse portion connected to said axial portion andlying immediately adjacent a maximum current region, said feed slotsbeing located at multiples of one-half wavelength along saidintermediate conductor with the transverse portions of even multiplefeed slots being reversed in direction from the transverse portions ofodd multiple feed slots;

a tubular outer conductor substantially coaxial with and receiving saidintermediate conductor and having an axial radiating slot substantiallyparallel to said inner conductor, said radiating slot beingsubstantially a multiple of one-half wavelength long;

and second and third short means adjacent first and second ends of saidouter conductor and between said outer and intermediate conductors todefine a chamber around said intermediate conductor, said chamber beingsubstantially a multiple of one-half wavelength long and said secondshort means being substantially a multiple of one-half Wavelength beyondthe center of the endmost feed slot in said intermediate conductor.

2. The triaxial antena of claim 1, wherein said feed slots are generallyU-shaped with the center of the axial portions being immediatelyadjacent maximum voltage regions in said coaxial line, maximum currentregions being spaced at one-quarter wavelength intervals from saidmaximum voltage regions.

3. The triaxial antenna of claim 1, wherein said feed slots aregenerally Z-shaped.

4. The triaxial antenna of claim 3, wherein the center of the axialportions of said fed slots lie immediately adjacent maximum currentregions in said coaxial transmission line and wherein said transverseportions of said feed slots extend from ends of said axial portions backalong said axial portions toward said maximum current regions.

5. The triaxial antenna of claim 1, wherein said series of feed slotsdefine a single, elongated slot comprising a plurality of substantiallyhalf wavelength feed slots joined end to end.

6. The triaxial antenna of claim 5, wherein said transverse portionsextend axially from the opposite ends of sadi axial portions.

7. The triaxial antenna of claim 1, including a plurality 5 of series offeed slots spaced equally from each other around said intermediateconductor.

8. The triaxial antenna of claim 7, wherein said feed slots aregenerally U-shaped with centers of said axial portions immediatelyadjacent maximum voltage regions in said coaxial line.

9. A transversely polarized triaxial antenna, comprising:

a shorted coaxial TEM mode transmission line including an innerelongated conductor, a tubular intermediate conductor substantiallycoaxial with and receiving said inner conductor, and first electricalshort means adjacent a first end of said intermediate conductor andbetween said intermediate and inner conductors responsive to electricalenergy applied to a second end of said line for setting up a standingwave pattern in said coaxial line including separate series of halfwavelength spaced maximum current and voltage regions;

said intermediate conductor including a complex feed slot substantiallyone-half wavelength long and having an axial portion substantiallyparallel to said inner conductor and a transverse portion connecting tosaid axial portion and lying immediately adjacent a maximum currentregion; tubular outer conductor substantially coaxial with and receivingsaid intermediate conductor and having an axial radiating slotsubstantially parallel to said inner conductor, said radiating slotbeing substantially a multiple of one-half wavelength long; and secondand third short means adjacent first and second ends of said outerconductor and between said outer and intermediate conductors to define achamber around said intermediate conductor, said chamber beingsubstantially a multiple of one-half wavelength long and said secondshort means being substantially a multiple of one-half wavelength beyondthe center of said feed slot.

References Cited UNITED STATES PATENTS 2,954,556 9/1960 Yang 343-770 XR3,106,713 10/1963 Hiroshi Murata et al. 343770 HERMAN KARL SAALBACH,Primary Examiner.

M. NUSSBAUM, Assistant Examiner.

9. A TRANSVERSELY POLARIZED TRIAXIAL ANTENNA, COMPRISING: A SHORTEDCOXIAL TEM MODE TRANSMISSION LINE INCLUDING AN INNER ELONGATEDCONDUCTOR, A TUBULAR INTERMEDIATE CONDUCTOR SUBSTANTIALLY COAXIAL WITHAND RECEIVING SAID INNER CONDUCTOR, AND FIRST ELECTRICAL SHORT MEANSADJACENT A FIRST END OF SAID INTERMEDIATE CONDUCTOR AND BETWEEN SAIDINTERMEDIATE AND INNER CONDUCTORS RESPONSIVE TO ELECTRICAL ENERGYAPPLIED TO A SECOND END OF SAID LINE FOR SETTING UP A STANDING WAVEPATTERN IN SAID COXIAL LINE INCLUDING SEPARATE SERIES OF HALF WAVELENGTHSPACED MAXIMUM CURRENT AND VOLTAGE REGIONS; SAID INTERMEDIATE CONDUCTORINCLUDING A COMPLEX FEED SLOT SUBSTANTIALLY ONE-HALF WAVELENGTH LONG ANDHAVING AN AXIAL PORTION SUBSTANTIALLY PARALLEL TO SAID INNER CONDUCTORAND A TRANSVERSE PORTION CONNECTING TO SAID AXIAL PORTION AND LYINGIMMEDIATELY ADJACENT A MAXIMUM CURRENT REGION; A TUBULAR OUTER CONDUCTORSUBSTANTIALLY COAXIAL WITH AND RECEIVING SAID INTERMEDIATE CONDUCTOR ANDHAVING AN AXIAL RADIATING SLOT SUBSTANTIALLY PARALLEL TO SAID INNERCONDUCTOR, SAID RADIATING SLOT BEING SUBSTANTIALLY A MULTIPLE OFONE-HALF WAVELENGTH LONG;